The present invention relates to cutting devices, particularly, a relatively high speed cutter to be used on a moving web.
In the past, traveling webs have been cut at a station in which web travel has been halted. A knife blade acting against a supporting edge moves in a generally vertical path with respect to a horizontally moving web. The blade may be angled so that as the blade moves in the vertical direction, the area of intersection of the blade with the backing plate appears to translate in a direction transverse to the direction of web travel.
This angled cutting, which can be found in most paper cutters, and for example, the guillotine, only cuts a small increment of the web at any given time in the travel of the blade. Accordingly, less cutting force is required.
An alternative cutting device for use with a moving web also uses a "travelling" cutting edge. A matched pair of rollers are positioned with their axes transverse to the path of the web. One of the rollers has a blade that is embedded in the roller. The opposing roller may have either a matching plate or may be of a resilient material that deforms under the blade. As the roller rotates, the knife edge effectively traverses the width of the web. Since the web is moving, the rollers may be angled slightly in the direction of web travel so that cut will be at right angles to the web edge.
Such a device must be provided with some mechanism that permits it to "idle" or remain out of engagement with the web until the web is to be cut into the desired length. This may require bringing one or both rollers in and out of engagement with the web. Other approaches may require that the rollers be provided with clutches that can be selectively engaged when a cut is required.
Further, prior art web cutting systems required blades which came to a sharp cutting edge with either a single or double taper. Such blades quickly dull and are dangerous to handle. Further, such blades present a substantial hazard to workers because of the sharpness of the cutting edge.
Scissors or shears rely on relatively thicker blades with a substantially right angled edge. The blades are joined at a pivot point and are mounted to be intersecting at a shallow angle. Because of the flexibility of the blades, the point of intersection travels outward from the pivot point with the blades displacing each other sufficiently to allow a cutting intersection to travel to the free ends of the blades.
It would be desirable to adapt the "scissors-type" cutting action of shears to the problem of cutting a traveling web. In fact, if a flexible web is driven to the cutter and the cutting action is rapid enough, the web can be momentarily halted while the cutter is employed. The cut section can be removed and the web can then continue until another cut is commanded.